1. Field of the Invention
The present invention relates to an input device of a two orthogonal polarized-wave waveguide type, and a radio wave receiving converter and an antenna device using the input device, and particularly relates to an input device of a two orthogonal polarized-wave waveguide type, mainly used in a radio wave feeder unit of a receiving converter that is mounted on a satellite reception parabolic antenna.
2. Description of the Background Art
FIG. 9 is a cross-sectional view showing a configuration of a conventional radio wave receiving converter. FIG. 10 is a cross-sectional view taken along a line X-X in FIG. 9, while FIG. 11 is a cross-sectional view taken along a line XI-XI in FIG. 9. In FIGS. 9-11, the radio wave receiving converter is provided with a chassis 51 integrally formed by die-casting that mainly uses aluminum, zinc, and others.
Chassis 51 includes a circular waveguide unit 52, a horn unit 53, a board holding unit 54, and a terminal holding unit 55. Circular waveguide unit 52 has a waveguide element 52a having a circular cross-sectional shape and a prescribed length. A rear end of waveguide element 52a is closed by a reflection wall 52b. 
Circular waveguide unit 52 is provided with two feed probes 60 and 61 for receiving a vertically-polarized wave V and a horizontally-polarized wave H, respectively, and a reflection rod 62 for reflecting vertically-polarized wave V. Tip portions of feed probes 60 and 61 protrude into waveguide element 52a from an inner peripheral wall of circular waveguide unit 52 in directions parallel with polarized waves V and H, respectively. Reflection rod 62 is provided to penetrate waveguide element 52a in the direction parallel with polarized wave V.
A proximal end portion of feed probe 60 is fixed to a through hole formed on an upside of waveguide element 52a with an insulating member interposed therebetween, and protrudes from an upper surface of circular waveguide unit 52. Feed probe 61 is bent at a right angle, and its proximal end portion is fixed to a through hole formed on the upside of waveguide element 52a with an insulating member interposed therebetween, and protrudes from the upper surface of circular waveguide unit 52.
Horn unit 53 is provided at an opening of circular waveguide unit 52 and introduces polarized waves V and H into circular waveguide unit 52. Board holding unit 54 is formed into a tray-like shape having a rectangular rim 54a, and has one end portion provided on circular waveguide unit 52, and the other end portion protruding rearward from circular waveguide unit 52. Board holding unit 54 accommodates a circuit board 63 with a ground plane facing downward. Each of the proximal end portions of feed probes 60 and 61 penetrates a hole in circuit board 63, and is connected by soldering, for example, to a circuit provided at a surface of circuit board 63.
Terminal holding unit 55 is provided on a downside of the other end portion of board holding unit 54. Terminal holding unit 55 has an output terminal 64 fixed thereto. Output terminal 64 is connected to circuit board 63 via a line introduced into a through hole formed in board holding unit 54. Circuit board 63 has a conversion circuit mounted thereon for amplifying and frequency-converting polarized waves V and H received at feed probes 60 and 61. An output signal of the conversion circuit is provided to a television tuner via output terminal 64.
A lid-like metal frame 65 is provided to cover an inside of rim 54a of board holding unit 54. Metal frame 65 has a rim and a septum 65a both of which are brought into contact with a ground plane provided at the surface of circuit board 63, and has an end portion fixed to a bottom surface of board holding unit 54 with a plurality of screws 66. This allows circuit board 63 and metal frame 65 to be fixed to chassis 51, and the circuit provided at the surface of circuit board 63 to be shielded by metal frame 65. Furthermore, septum 65a of metal frame 65 prevents each of the received polarized waves from leaking to a circuit intended for another polarized wave.
An operation of the radio wave receiving converter will hereinafter be described. Polarized waves V and H, which are collected at horn unit 53, propagate through waveguide element 52a in circular waveguide unit 52, and are reflected at reflection rod 62 and reflection wall 52b, respectively. Vertically-polarized wave V reflected at reflection rod 62 is received by feed probe 60, transmitted to a microstrip line of circuit board 63, amplified and frequency-converted at a high-frequency circuit in a subsequent stage into an intermediate frequency signal, and transmitted to the tuner via output terminal 64. Horizontally-polarized wave H reflected at reflection wall 52b is received by feed probe 61, transmitted to a microstrip line of circuit board 63, amplified and frequency-converted at a high-frequency circuit in a subsequent stage into an intermediate frequency signal, and transmitted to the tuner via output terminal 64.
FIG. 12 is a cross-sectional view showing a configuration of another conventional radio wave receiving converter, and is to be compared with FIG. 10. In FIG. 12, the radio wave receiving converter differs from the radio wave receiving converter in FIGS. 9-11 in that two circular waveguide units 52 are provided. Two circular waveguide units 52 are arranged in parallel at a prescribed spacing, and formed integrally. Each of circular waveguide units 52 is provided with feed probes 60 and 61. Board holding unit 54, circuit board 63, and metal frame 65 are provided in a manner common to two circular waveguide units 52. With this radio wave receiving converter, it is possible to receive vertically-polarized waves V1, V2 and horizontally-polarized waves H1, H2 transmitted from two adjacent satellites.
FIG. 13 is a cross-sectional view showing a substantial part of still another conventional radio wave receiving converter, and is to be compared with FIG. 10. Such a radio wave receiving converter is disclosed in, for example, Japanese Patent Laying-Open No. 10-261902. With reference to FIG. 13, this radio wave receiving converter differs from the radio wave receiving converter in FIGS. 9-11 in that a board holding unit 70, a circuit board 71, and a metal frame 72 are additionally provided. In the conversion circuit mounted on circuit board 63, a circuit portion exclusively used for receiving horizontally-polarized wave H is mounted on circuit board 71. Board holding unit 70 is provided vertically to board holding unit 54 so as to hold circuit board 71 in a direction vertical to horizontally-polarized wave H.
Board holding unit 70 is formed into a tray-like shape having a rectangular rim 70a, and provided on the left side of circular waveguide unit 52 in the drawing. Board holding unit 70 accommodates circuit board 71 with a ground plane facing the right side. Feed probe 61 is not bent, and its proximal end portion penetrates a hole in circuit board 71 and connected by soldering, for example, to a circuit provided at a surface of circuit board 71.
Lid-like metal frame 72 is provided to cover an inside of rim 70a of board holding unit 70. Metal frame 72 has a rim brought into contact with a ground plane provided at the surface of circuit board 71, and has an end portion fixed to a bottom surface of board holding unit 70 by a screw 73. This allows circuit board 71 and metal frame 72 to be fixed to chassis 51, and the circuit provided at the surface of circuit board 71 to be shielded by metal frame 72. Metal frames 65 and 72 prevent the received polarized waves from leaking to circuits intended for other polarized waves, respectively. An operation of the radio wave receiving converter is the same as that of the radio wave receiving converter shown in FIGS. 9-11, and hence the description thereof will not be repeated.
As described above, in the conventional radio wave receiving converter shown in FIGS. 9-12, a plurality of received polarized waves V and H are amplified and frequency-converted at the single circuit board 63, and each of the polarized waves is prevented from leaking to a circuit intended for another polarized wave, by bringing septum 65a of metal frame 65 into the ground plane of circuit board 63 and shielding the circuits.
However, chassis 51 and metal frame 65 are fabricated by die-casting, and hence they deform owing to variations in casting condition and the like. This causes a problem of nonuniform contact between septum 65a of metal frame 65 and the ground plane on circuit board 63 and thus deterioration in shielding effect, and leakage of each of the polarized waves to a circuit intended for another polarized wave and thus deterioration in cross polarization characteristic. This problem becomes prominent when a die-casting die wears, and hence the die requires frequent renewal, which entails enormous cost for the die.
In the radio wave receiving converter shown in FIG. 12, in particular, each of the polarized waves V1, V2, H1, and H2 must be shielded, and metal frame 65 inevitably grows in size. Accordingly, if metal frame 65 suffers the slightest deformation such as warpage, the polarized waves disadvantageously leak. Furthermore in recent years, reception from a plurality of satellites, a multi-output converter, and the like have often been adopted, so that signals are often switched at a switch circuit in a subsequent stage of the circuit. Mixture of a cross polarization characteristic and an isolation characteristic of the switch circuit affects the quality of the signals, and hence improvement in cross polarization characteristic on the periphery of a waveguide feeder unit is demanded.
In contrast, in the radio wave receiving converter in FIG. 13, circuit board 63 for receiving polarized wave V and circuit board 71 for receiving polarized wave H are separately provided, and accordingly a cross polarization characteristic is improved. However, bottom surfaces of board holding units 54 and 70 are orthogonal to each other, so that one of the bottom surfaces must be formed with a sliding insert in the design of a die. This causes a problem of complexity of the die, and hence cost increase.